The objective of this grant is to study the acute health effects of selected sulfate, nitrate and hydrocarbon aerosols under controlled conditions of particle size, concentration, temperature and relative humidity. During this coming year, we plan to measure changes in pulmonary functions in squirrel monkeys exposed to polydisperse sulfuric acid aerosols over a range of mass median aerodynamic diameters (MMAD), relative humidities and concentrations. The dependency of the effect of other irritant sulfate and nitrate salts on the MMAD of the polydisperse size distribution may also be investigated. Common organic acids in the atmospheric aerosol will be generated in pure form to assess their acute irritancy. A parallel phase of this research involves developing better mathematical models for estimating the transport, deposition and tissue uptake of the hygroscopic aerosols. Improved methods of scaling or relating acute dose-response data between different animal species and humans will also be investigated in this phase.